The formation mechanism of the friction stir welds

Based on the experimental observation, a new formation model of the friction stir welds is suggested. The formation of welds is a process in which a groove is formed when the stir tool moves along the welding line and then is filled behind the stir pin. During this process, the metal flowed into the groove consists of four parts, that is, the metal flowing along the threads on the pin surface, the metal from the shoulder downward to the groove behind the pin, and the metal in front of the pin flowing from two sides of the pin into the groove behind the pin. These flowing metals will contact each other in the groove and join metallurgically by means of the diffusion bonding mechanism. By means of this formation mechanism, the stir tool and welding parameters could be designed more correctly and the welding flaws could be forecasted previously.